Reticular web having reinforced selvages and method and apparatus for manufacturing the same

Abstract

 A reticular web (9) of thermoplastic resin composed of split or slit fibres comprises a pair of laterally spaces selvages (24, 25) and a middle portion (23) therebetween.
In order to dimensionally stabilise the selvages (24, 25) each selvage (24, 25) has at least one dimensionally stable thread (26, 27) attached thereto along the length thereof.
The invention also includes method and apparatus for producing the web (9).

Description

[0001] The present invention relates to a reticular web of thermoplastic resin composed of split or slit fibers integrally joined together at intervals along the length thereof which has reinforced and dimensionally stabilized selvages, and a method and apparatus for continuously manufacturing such a web.

[0002] Reticular webs of thermoplastic resin composed of split or slit fibers integrally joined together at intervals along the length thereof or having longitudinal discrete cuts are difficult to handle when spread transversely since the fibers or meshes are positionally unstable and hence tend to be shifted under tension as when the web is reeled out. More specifically, the web undergoes undue spreading along selvages thereof which are gripped by cloth guiders for guiding the web while the latter is being paid out, with the result that the web will have irregular meshes widthwise. To cope with this difficulty, such reticular webs, upon having been transversely spread, are customarily bonded together warpwise and weftwise in layers so as to be marketable as stable nonwoven web materials.

[0003] There has been a need for reticular webs to be available as such in the market so that they can be used as, for axample, outer layers in a laminate having an intermediate film layer or as reinforcing layers for use in combination with pulp, paper, film and the like.

[0004] The present invention seeks to provide a reticular web of split or slit fibres which is dimensionally stabilized along the selvages thereof for easy handling in use.

[0005] The invention further seeks to provide a method and apparatus for manufacturing such a fibrous reticular web.

[0006] According to a first aspect of the invention, there. is provided a reticular web of thermoplastic resin composed of split or slit fibres, the recticular web comprising a pair of laterally spaced selvages and a middle portion extending therebetween characterised in that each selvage has at least one dimensionally stable thread attached thereto along the length thereof.

[0007] According to a second aspect of the invention, there is provided a method of manufacturing a reticular web having reinforced and dimensionally stabilised selvages characterised in that at least one dimensionally stable thread is attached to each selvage along the length thereof.

[0008] According to a third aspect of the invention, there is provided apparatus for manufacturing a reticular web, having reinforced and dimensionally stabilised selvages, characterised in that means are provided for attaching at least one dimensionally stable thread to each selvage along the length thereof.

[0009] The invention will now be described in greater detail by way of example, with reference to the drawings, wherein:-

Figure 1 is a schematic side elcvational view of an apparatus according to the present invention;

Figure 2 is an enlarged front elevational view of a system of nip rollers for transversely spreading the selvages of a fibrous reticular web;

Figure 3 is a fragmentary perspective view of one of the nip rollers shown in Figure 2;

Figure 4 is an enlarged fragmentary view of a transversely spread reticular web;

Figure 5 is a cross-sectional view of a take-up roll;

Figure 6 is an enlarged front elevational view showing a web spreader according to an embodiment;

Figure 7 is a side elevational view of the web spreader shown in Figure 6;

Figure 8 is a fragmentary perspective view of a web spreader according to another embodiment;

Figure 9 is a cross-sectional view of the web spreader of Figure 8;

Figure 10 is an enlarged fragmentary front elevational view of a web spreader according to still another embodiment; and

Figure 11 is a side elevational view of the web spreader shown in Figure 10.

[0010] Figure 1 shews an apparatus 10 for manufacturing a nonwoven reticular web 11 having reinforced, dimensionally stabilized selvages. A longitudinally stretched, nonwoven reticular web 9 of thermoplastic resin composed of split or slit fibers integrally joined together at intervals along the length thereof is longitudinally fed around a guide roller 12 toward cloth guiders 13 (Figures 1 and 2), which laterally spread the web 9 by 5 - 10% of the width of the starting web 9. The web 9 is then caused to travel around nip or pinch rollers 14, 15, 16 rotatively driven by a motor (not shown).

[0011] The uppermost one 16 of the nip rollers comprises a barrel including, as best shown in Figures 2 and 3, a larger-diameter middle portion 17 and a pair of smaller-diameter end portions 18, 19 between which the middle portion 17 is disposed. An annular shoulder 20 is defined between the middle portion 17 and each of the end portions 18, 19 and has herein a series of holes or orifices 21 opening axially of the roller 16. The middle portion 17 is coupled to an air compressor (not shown) for blowing an air blast through the holes 21 axially over the smaller-diameter end portions 18, 19.

[0012] The web 9 travels between the nip rollers 14, 15, 16 and is wrapped partly around the roller 16, only the middle portion 23 (Figure 2) of the web along its length being nipped between the nip roller 15 and the larger-diameter middle portion 17 of the nip roller 16 and the opposite selvages or longitudinal marginal edges 24, 25 of the web 9 over-hanging the smaller-diameter end portions 18, 19, respectively, therearound. An air blast discharged through the holes 21 in the shoulders 20 impinges upon the selvages 24, 25 to spread the fibers thereof transversely away from each other, whereby the selvages 24, 25 are caused to shrink longitudinally or shorten until they are brought radially inwardly into contact with the surfaces of the smaller-diameter end portions 18, 19. Upon contact with the smaller-diameter end portions 18, 19, the selvages 24, 25 are forced to travel therewith in an arcuate path in which they are prevented from being laterally spread further. Thus, the amount of transverse spreading of the selvages 24, 25 is automatically controlled dependent on the diametrical difference between the roller portions 17 and 18, 19.

[0013] At least one, or preferably a pair of dimensionally stable threads 26, 27 (Figures 1 and 4) such, for example, as those of flat yarn which are coated with hot-melt adhesive are guided around electrically heated pulleys 28, 29 disposed on the smaller-diameter end portions 18, 19 of the nip roller 16. As the threads 26, 27 are fed around the pulleys 28, 29, the threads 26, 27 are bonded by melted adhesive to the transversely spread selvages 24, 25 on the smaller-diameter end portions 18, 19, as best illustrated in Figure 4.

[0014] Upon having been thus transversely spread and dimensionally stabilized along the selvages 24, 25 the web 9, which is longer at the middle portion 23 than at the selvages 24, 25, is directed toward cloth guiders 31 (one set shown) which are spaced laterally from each other by a distance several times greater than the width of the middle web portion 23 as substantially unspread. On advancing movement of the web 9, the reinforced selvages 24, 25 are gripped by the cloth guiders 31, whereupon the middle portion 23 of the web 9 is transversely spread and at the same time longitudinally shrunk or shortened to an extent determined by the amount of lateral spreading. In the illustrated embodiment, the amount of transverse spreading of the middle portion 23 effected by the cloth guiders 31 is made smaller than that of the selvages 24, 25. The remaining excessive length of the middle portion 23 of the web 9 is removed by causing the web 9 to travel around a pair of heated drums 32, 33 on which the middle portion 23 is additionally longitudinally heat-shrunk until it has substantially the same length as that of the selvages 24, 25. The laterally spread and heat-treated web 11 is substantially uniform in length and reticular structure. With the width of each of the fibers in the reticular web being on the order of 1 mm or greater, each fiber tends to rise obliquely when the web is transversely spread. The greater the width of each fiber, the more the fiber undergoes such tendency. However, the fibers are held flatwise against the heated drums 32, 33 and thereby heat-set in stabilized flat arrangement.

[0015] Where the starting reticular web has a warpwise diagonal length of individual fibers preferably ranging from 30 mm to 50 mm, the web is longitudinally shortened only by several per cent or less when it is transversely spread two to three times. Additional heat shrinkage of the web, if limited to several to about 10%, would enhance thermal stability rather than lower mechanical strength thereof.

[0016] The treated web 11, upon having left the heated drum 33, may be wound up as an end product for shipment. However, where the treated web 11 is to be bonded to paper or be combined with pulp, the web 11 is coated with hot-melt adhesive or emulsion adhesive contained in an adhesive container 34 by a kiss roller 35 partly immersed in the adhesive in the container 34. The web 11 is then caused to travel around rollers 36, 37, 38, 39 for uniform distribution and drying and cooling of the coated adhesive before being guided by guides 40 and a guide roller 41 toward a take-up reel 42.

[0017] As shown in Figure 5, the web 11 is wound as a roll 43 on the take-up reel 42.

[0018] Each of the selvages 24, 25 including the threads 26, 27 has a basis weight which is substantially the same as or smaller than that of the middle portion 23. More specifically, it has been customary practice to reinforce paper or film with reticular webs of fibers having a tensile strength at freak of 4 - 5g/denier which are arranged warpwise and weftwise in layers with a basis weight of either 20 - 25g/m² for light reinforcement or 40 - 60g/m² for heavy-duty reinforcement. For light reinforcement, therefore, a reticular web produced from a stretched film having a thickness of 20 microns and a basis weight of 20g/m² before lateral spreading is transversely spread two times until the web has a basis weight of about 10g/m², which corresponds to 900 denier per 10 mm of width. Where the middle portion of the web has that basis weight, the selvages of the web are transversely spread four times until their basis weight corresponds to 450 denier per 10 mm of width. Two parallel flat yarns of 200 denier spaced 10 mm from each other are bonded warpwise to each of such laterally spread selvages, with the result that each selvage including the bonded yarns has a basis weight corresponding to 850 denier per 10 mm of width which is slightly smaller than that of the middle portion of the web. Alternatively, each of the selvages is transversely spread six times and two reinforcement threads of 200 denier are bonded to each selvage. Each such selvage including the two threads has a basis weight equivalent to 550 denier per 10 mm of width, which is substantially half that of the middle portion of the web. With such an arrangement, the roll 43 is wound more tightly at the middle portion 23 than at the selvages 24, 25 so that the roll 43 will be resistant to forces tending to tumble or collapse itself and hence can be easily handled during shipment and storage for example. The spread web 11 when unwound is table in dimension especially at the selvages 24, 25, which can reliably be guided or supported by suitable guides during subsequent processing.

EXAMPLE 1

[0019] A tubular film of high-density polyethylene (HDPE) having a thickness of 0.06 mm and a diameter of 480 mm upon, forming by melt extrusion was water-quenched at a speed of 25 m/min. and slit open longitudinally into an elongate sheet or web having a width of 1.5m. The sheet was cut by a rotary cutter to form therein discrete cuts or incisions in a staggered arrangement, spaced 3 mm laterally and longitudinally from each other, and having a length of 10 mm, and then was fed into a bath of hot water at 100°C, in which the web was longitudinally stretched 8.5 times the original length to a width of 510 mm and was taken off by nip rollers onto heated drums, on which the web was dried. The web was then transversely spread to a small degree by the cloth guiders 13 as shown in Figures 1 and 2 to a width of 620 mm and was caused to travel around the nip rollers 14, 15, 16, the roller 16 having middle barrel portion of 600 mm in length. Selvages of the web each having a width of 10 mm were transversely spread by an air blast discharged through the holes 21. Two HDPE parallel flat yarns of 200 denier spaced 10 mm from each other and coated with ethylene-vinyl acetate copolymer hot-melt adhesive were bonded warpwise to each of the transversely spread selvages. The web was transversely spread at the middle portion by the guiders 31 two times to a width of 1.2m, and the web was caused to travel around the heated drums 32, 33 at a speed of 200m/min., to thereby heat-shrink the middle web portion in the longitudinal direction. The web was then coated with hot-melt adhesive by the kiss roller 35, and the adhesive was evenly respread on the heated drums 36 - 38, followed by cooling on a cooling drum 39. The resultant spread web was 1,250 mm wide and had a basis weight of 10g/m², and was wound around the take-up reel 42 at a speed of 200m/min.

EXAMPLE 2

[0020] Two pieces of the sheet having a width of 1.5m obtained in EXAMPLE 1 w_ere separately given longitudinal discrete cuts and longitudinally stretched six times the original length in a hot-water bath, and then the webs were superposed on each other and additionally longitudinally stretched again to 8.5 times the original length. The longitudinally stretched webs as superposed were dried and thereafter processed as in EXAMPLE 1 into a laterally spread web product having a width of 1.25 mm and a basis weight of 20g/m², which is twice that of the produce obtained in EXAMPLE 1, and were then wound up into a roll at a speed of 200m/min.

EXAMPLE 3

[0021] Two superposed webs were processed substantially in the same manner as in EXAMPLE 2, except that the middle web portion was transversely spread four times. The obtained web product had a basis weight of 10g/m² and a width of 2.5m.

[0022] As shown in Figures 6 and 7, a pair of nozzles 46, 47 according to another embodiment are disposed adjacent to and directed toward the smaller-diameter portions 18, 19, respectively, of the nip roller 16. The nozzles 46, 47 are connected to a pipe 48 which is in turn connected to a source of compressed air (not shown) for blowing an air blast through the nozzles 46, 47 to the selvages 24, 25 of the reticular web 9. The nozzles 46, 47 continue to discharge the air blast toward the selvages 24, 25 for laterally spreading the latter onto the smaller-diameter roller portions 18, 19 of the nip roller 16.

[0023] Figures 8 and 9 illustrate still another embodiment in which a casing 50 surrounds a portion of each of the smaller-diameter portions 18, 19 of the roller 16. An air suction pump 51 is coupled to the casing 50 to develop air suction in the casing 50 so that the selvages 24, 25 of the reticular web 9 can be transversely spread in opposite outward directions within the casings 50, respectively.

[0024] According to still another embodiment as illustrated in Figures 10 and 11, a rotatable brush 53 supported on a shaft 54 is disposed adjacent to each of the smaller-diameter portions 18, 19 of the nip roller 16. The brush 53 has a multiplicity of wires 55 projecting radially outwardly for engaging and spreading the selvages 24, 25 onto the smaller-diameter roller portions 18, 19 upon rotation of the brushes 53.

Claims

1. A reticular web of thermoplastic resin composed of split or slit fibres, the recticular web (9), comprising a pair of laterally spaced selvages (24, 25) and a middle portion (23) extending therebetween,
characterised in
that each selvage (24, 25) has at least one dimensionally stable thread (26, 27) attached thereto along the length thereof.

2_. A reticular web as claimed in claim 1 wherein each of the selvages is transversely spread to a greater extent than the middle portion (23), each of the selvages (24, 25) has a basis weight which is substantially the same as or smaller than that of the middle portion (23), and the middle portion (23) has substantially the same length as the said selvages (24, 25) as a result of being heat-shrunk, so that said selvages (24, 25) are dimensionally more stable than said middle portion (23) for easy handling of said reticular web (9).

3. A reticular web as claimed in claim 1 or 2, wherein the thread (26, 27) is adhesively bonded to the fibres of the selvages (24, 25).

4. A reticular web as claimed in claim 1, 2 or 3, wherein the thread (26, 27) comprises flat yarn.

5. A method of manufacturing a reticular web having reinforced and dimensionally stabilised selvages (24, 25) characterised in
that at least one dimensionally stable thread (26, 27) is attached to each selvage (24, 25) along the length thereof.

6. A method as claimed in claim 5, wherein the method also comprises feeding a longitudinally stretched reticular web ( 9) of thermoplastic resin composed of warpwise split or slit fibres and transverly spreading opposite selvages (24, 25) only of the reticular web (9) prior to the attachment of the dimensionally stable threads (26, 27) and thereafter transversely spreading the middle portion (23) of the reticular web (9) between the selvages (24, 25) to an extent which is smaller than that of the selvaves (24,25) and heat-shrinking the middle portion (23) longitudinally until it has substantially the same length as that of the selvages, (24, 25) with each selvage (24, 25) having a basis weight which is substantially the same as or smaller than that of the middle portion (23).

7. A method as claimed in claim 6, wherein the opposite selvages (24, 25) of the reticular web (9) are transversely spread by blowing with an air blast.

8. A method as claimed in claim 6, wherein the opposite selvages (24, 25) of the reticular web (9) are transversely spread by developing air suction thereon.

9. A method as claimed in claim 6, wherein the opposite selvages (24, 25) of the reticular web (9) are transversely spread by a rotating brush held thereagainst.

10. A method as claimed in claim 5, wherein the method also comprises feeding a longitudinally stretched reticular web (9) of themoplastic resin composed of warpwise split or slit fibres partly wrapping the reticular web (9) around a roller (16) having a largerrdiameter middle portion (17) and opposite smaller-diameter end portions (18, 19) and simultaneously with the wrapping step, transversely spreading the opposite selvages (24, 25) of the reticular web (9) until they are longitudinally shortened and wrapped around the smaller-diameter portions (18, 19) of the roller (16) prior to attachment of the dimensionally stable threads (26, 27) and thereafter transversely spreading the middle portion (23) of the reticular web (9) to an extent which is smaller than that of the transversely spread selvages (24, 25) and heat-shrinking the middle portion (23) longitudinally on a hot drum (32, 33) until the middle portion (23) has substantially the same length as that of the selvages (24, 25), with each selvage (24, 25) having a basis weight which is substantially the same as or smaller than that of the middle portion (23).

11. A method as claimed in claim 10, wherein the opposite selvages (24, 25) of the reticular web (9) are transversely spread by an air blast blown thereonto through holes (21) in a shoulder (20) between the larger-diameter portions (17) and the smaller-diameter portions (18,19) of the roller (16).

12. A method as claimed in claim 10, wherein the opposite selvages (24, 25) of the reticular web (9) are transversely spread by blowing an air blast thereonto through a nozzle (46, 47).

13. A method as claimed in claim 10, wherein the opposite selvages (24, 25) of the reticular web (9) are transversely spread by developing air suction in a casing (50) partly covering each of the smaller-diameter portions (18, 19) of the roller (16).

14. A method as claimed in claim 10, wherein the opposite slevages (24, 25) of the reticular web (9) are transversely spread by a rotating brush (53) disposed adjacent to each of the smaller-diameter portions (18, 19) of the roller (16).

15. Apparatus for manufacturing a reticular web, having reinforced and dimensionally stabilised selvages (24, 25) characterised in
that means (26, 28, 29) are provided for attaching at least one dimensionally stable thread (26, 27) to each selvage (24, 25) along the length thereof.

16. An apparatus as claimed in claim 15, wherein the apparatus also comprises means (12, 13, 14) for feeding a longitudinally stretched reticular web (9) of thermoplastic resin composed of warpwise split or slit fibres, first means (16) for transversely spreading opposite selvages (24,25) only of the reticular web (9), second means (31) for transversely spreading the middle portion (23) of the reticular web (9) between the selvages(24, 25) to an extent which is smaller than that of the selvages (24,25) and means (32,33) for heat-shrinking the middle portion (23) longitudinally until it has substantially the same length as that of the selvages (24, 25), with each selvage (24,25) having a basis weight which is substantially the same as or smaller than that of the middle portion (23).

17. An apparatus as claimed in claim 16, wherein the first means comprises a roller (16) having smaller-diameter end portions (18, 19) for supporting the selvages (24, 25) respectively, and a larger-diameter middle portion (17) between the smaller-diameter end portions (18, 19) for supprting the middle portion (23) of the web (9) and means (21, 46, 47, 50, 53) for forcing the selvages (24, 25) laterally away from each other until they are longitudinally shortened into contact with the smaller-diameter end portions (18, 19).

18. An apparatus as claimed in claim 17, wherein the forcing means comprises an annual shoulder (20) disposed between the larger-diameter middle portion (17) of the roller (16) and each smaller-diameter end portion (18, 19) thereof and having a series of holes (21) in the shoulder (20) for blowing an air blast laterally toward the web selvage (24, 25).

19. An apparatus as claimed in claim 17, wherein the forcing means comprises a nozzle (46, 47) disposed adjacent to each of the smaller-diameter end portions (18, 19) for blowing an air blast laterally toward the web selvage (24, 25).

20. An apparatus as claimed in claim 17, wherein the forcing means comprises a casting (50) partly covering each of the smaller-diameter end portions (18, 19) and a pump (51) coupled to the casing (50) for developing air suction in the casing (50).

21. An apparatus as claimed in claim 17, wherein the forcing means comprises a rotatable brush (53) disposed adjacent to each of the smaller-diameter end portions (18, 19) for engagement with the web selvage (24, 25).

Drawing